Text: Maxwell wrote: "There are physical quantities of another kind which are related to directions in space, but which are not vectors. Stresses and strains in solid bodies are examples of these, and so are some of the properties of bodies considered in the theory of elasticity and in the theory of double refraction. Quantities of this class require for their definition nine numerical specifications. They are expressed in the language of quaternions by linear and vector functions of a vector." "Not that when ExH=O (the Poynting vector is zero), the EM energy may still be present; it is merely not translating. It can be present as infolded stress, which is gravitational and a local curvature of spacetime. This was captured by Maxwell in his quaternion theory, but not by Heaviside in his vector theory." See T.E. Bearden, Maxwell's Original Quaternion Theory was a Unified Field Theory of Electromagnetics and Gravitation, Proceedings, Interntional Tesla Society Symposium, Colorado Springs, CO, 1988.

See Also: QUATERNION; FULL HARMONIC CHORD, TRIUNE STREAMS; POYNTING; SCALAR; UNDIFFERENTIATED; POLARITY; POLARIZATION

Source: 132